fix issue of inconsistent size

Author: Langwen Huang

src/differentiation/compute_jacobian_ad.jl

@@ -120,7 +120,8 @@ function forwarddiff_color_jacobian(f,x::AbstractArray{<:Number},jac_cache::Forw
             for j in 1:chunksize
                 col_index = (i-1)*chunksize + j
                 (col_index > ncols) && return J
-                J = J + mapreduce(i -> i==col_index ? partials.(vec(fx), j) : zeros(nrows), hcat, 1:ncols)
+                Ji = mapreduce(i -> i==col_index ? partials.(vec(fx), j) : zeros(nrows), hcat, 1:ncols)
+                J = J + (size(Ji)!=size(J) ? reshape(Ji,size(J)) : Ji) #branch when size(dx) == (1,) => size(Ji) == (1,) while size(J) == (1,1)
             end
         end
     end